In general, an image forming apparatus is a peripheral device that may have the functionality of a copier, a printer, and/or a facsimile, for example, and which is capable of printing an image on a printing medium. Such an image forming apparatus can include an image forming unit and a fusing device. The image forming unit can include a photosensitive medium on which an electrostatic latent image can be formed, and a developing unit configured to develop the electrostatic latent image by using a developing agent. After the developed image is transferred to a printing medium, the fusing device can fuse the developed image to the printing medium by applying heat and pressure.
The fusing device can include a heat roller having a lamp heater and a pressure roller that is engaged with the heat roller to form a fusing nip. In the above-structured fusing device, because the thermal capacity of the heat roller can be high and all surfaces of the heat roller are heated, heating the fusing device to a predetermined fusing temperature may take a relatively long time. Moreover, the fusing nip is formed where the heat roller and the pressure roller are engaged with each other, and thus, the fusing nip has a relatively narrow width.